The mass of the top quark is a fundamental parameter of the Standard Model. Measurements of the top quark mass using events with one charged lepton and at least four jets in the final state are presented using data collected by the CMS experiment during the year 2011, in proton-proton collisions at the LHC at a centre-of-mass energy of 7 TeV. The complete kinematics of each event is reconstructed using a constrained fit. For each event a likelihood is calculated as a function of assumed value of top quark mass and the probability that the event is a top quark-antiquark
pair event or not.
